So I was driving out of Advanced Auto Parts parking lot and pulled over to tighten my exhaust bolts because I forgot to the day before. All was tight and I started to rev it a bit to make sure I got the popping and gargling sound back, which It did. I then gave it one more rev and noticed it stayed between 5 and 6 rpm for a few seconds and, Reduced Engine Power text started coming up. Turns out she needed engine coolant, fine, poured some in and went on my marry way. Had to speed up and she started bitching, I then pulled into a parking lot to let her cool off before checking the coolant, again, she wanted more to drink, so I poured more to keep her happy. Drove home and everything was okay, drove to wash her and vacuum her today and she was fine, all is well.

I just wanted to ask when is it a good time to check coolant, if one runs hard and tows a trailer? Is it wise to do an oil change after a situation like this? Does reducing the engine power do more harm than what the manual says? I wont lie, I have not changed/filled the coolant in at least 5 years until now towing a trailer and driving a bit rough with new CAI and exhaust and possibly a tuner/chip later on. I am guessing with the new stuff and towing I should check the coolant a lot sooner than normal?

Well, the coolant has never been checked since 2005 I believe. Doesn't fluid empty overtime? Also, there is no pool anywhere in the driveway or anywhere I park as I am always checking underneath before getting in.

It should not lose coolant, since the system is a closed type. You could check to weep hole on the water pump, it may be leaking a little there and not enough to make it to the ground before it evaporates from the heat of the engine. You could have the cooling system pressure tested, and that should reveal any leaks that are external by being able to see them. If the system will not hold pressure and you have no external leaks, you can bet you've got an internal coolant leak of some type (Head gasket or something).

I mean if it will not hold pressure when you perform a pressure test. You have to have a pressure testing tool. It's kind of like a bicycle tire air pump that attaches to the coolant bottle (where you put in the coolant) and it puts pressure in the system.

Ah, okay. Well then. I will pick up a pressure tester tomorrow afternoon. I figured the coolant was getting evaporated from not being taken care of for so many years and it being put to work. Ty for the advice/help.

I forgot to mention ( if it means anything ) that when this problem started, the coolant cap was EXTREMELY easy to open as it took one slight turn. Out of boredom I did some research on Google with coolant loss on the 5.3L and I came across a post where a guy had a bad cap and the coolant kept boiling over into the overflow tube and caused him to fill the coolant every 2 or 3 days. After changing his cap he hasn't had an issue with coolant loss for some thousand miles. So, just out of curiosity, I checked my cap and it's still good and much harder to take off since I've been closing it, myself. It's also more responsive than normal, other than me having to tighten the front left tire since my last brake change.